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released 13 security bulletins Tuesday, the biggest monthly patch rollout since February 2005, when the software giant released 12 security bulletins. Eight of this month's updates are critical and address vulnerabilities in Windows, Internet Explorer, Exchange, Media Player, PowerPoint and Word.

According to various security firms and published media reports, at least two pieces of exploit code target security holes Microsoft brought to light on Tuesday. Most of the other exploits involve flaws that the information security community had already been aware of, which were fixed in Tuesday's patch update.

Johannes Ullrich, chief research officer of the Bethesda, Md.-based SANS Internet Storm Center (ISC), outlined some of the exploits on the organization's Web site.

A second proof-of-concept exploit, also released by a penetration testing vendor to customers, targets flaws outlined in MS06-025, which fixes a pair of critical remote code-execution flaws affecting versions of Windows 2000, XP and Server 2003.

Vulnerability researchers typically distribute proof-of-concept exploit code so customers can write rules for intrusion defense systems (IDS) and vulnerability scanners, enabling them to detect new attacks. The code is also used for academic research. Microsoft has frowned on the practice, saying conceptual exploits can be tweaked for malicious purposes.